Vehicle manufacturers are increasingly implementing Passive Keyless Entry (PKE) systems and Passive Keyless Entry and Start (PKES) systems. A PKE system provides a user with the convenience of unlocking a vehicle door without physically touching a key or pressing any buttons on a key fob. A PKES system allows a user to both unlock and start his or her vehicle without physically touching a key or pressing any buttons on a key fob. These systems improve driver safety and provide convenience for the driver in that the vehicle key fob can remain stowed, for example, in his or her pocket or bag when approaching or preparing to start the vehicle. Unfortunately, PKE and PKES systems can be vulnerable to relay attacks. In a relay attack, the attackers place one relay attack station in proximity to the key and another relay attack station in proximity to the vehicle. The attackers can then relay messages between the key and the vehicle via the relay stations, enabling the vehicle to be opened and started even if the key is physically distant from the vehicle.